I'm assuming that you're referring to the Windows Explorer listing
of files, probably in detail view.

The blue files are compressed.

Let's talk about what that means, and how you can turn that display
on and off.

•

First let's show what the question is referring to:

This is a partial listing of the files in my "C:\Windows" folder.
You can see that some of the folders are displayed in blue, while
others are shown in the more common black.

In the NTFS file system, files and folders can be marked as
"compressed". This means that when the file is written to disk it is
compressed to take up less actual disk space. Files added to a folder
marked as compressed are similarly compressed.

Not all files can be compressed, or rather, not all files get
smaller when you compress them. I know that seems backwards, but if a
file is already compressed, then attempting to compress it a second
time can actually make it a little larger instead.

"I only compress files when a disk is running
low on space and it's impractical for me to get more space by other
means."

Many files these days are already compressed. The best examples are
most audio files like mp3 files, most picture files like the jpg files
that come off of your digital camera, and most video files that you
might get from your video camera or shows that you download.

That's one reason why file compression is typically off by default;
you don't want to just blindly start compressing everything, because
not everything should be compressed.

Another reason is that compression and decompression when the file
is written or read takes some extra CPU time. These days it's not
really a lot, but it can add up if the file is accessed a lot.

So what files are good candidates for compression? Archives of
things that aren't already compressed and that you don't access a lot are good candidates.

But then again, with the size of hard disks being what they are
theses days, I rarely compress files, as there's simply no need to add
yet another something to what happens when reading and writing files. I
only compress files when a disk is running low on space and it's
impractical for me to get more space by other means.

Let's look at how to adjust that Windows Explorer setting, and then
also how to actually compress files or folders.

In Windows Explorer click on Tools, Folder
Options and then the View Tab. In the
Advanced settings list scroll down until you see Show encrypted
or compressed NTFS files in color:

Make sure that's checked, or not, as you desire. (In case you're
wondering, encrypted files display in green when this option is
selected, and compressed files in blue.)

Now, as for compressing files or folders, simply
right-click on the file or folder you want to compress, click
on Properties, click on the Advanced
button, and you should see something like this:

Make sure that "Compress contents to save disk space" is checked as
appropriate and OK your way back out, and Windows will
compress the file or folder.

(Since you might be tempted, I recommend against Windows
built-in file encryption unless you truly understand the ramifications.
In a nutshell, it's tied to your Windows login, and if you ever lose
that you will lose the files or folders that you've
encrypted - permanently. If you need encryption, I recommend a solution
like TrueCrypt
instead.)

Leo A. Notenboom has been playing with computers since he
was required to take a programming class in 1976. An 18 year career as a programmer at Microsoft soon followed.
After "retiring" in 2001, Leo started Ask Leo! in 2003 as a place for answers
to common computer and technical questions. More about Leo.

Not what you needed?

You may also be interested in:

Should I use
Windows File Compression? Windows File Compression automatically
compresses files so that they take up less space. In the best
circumstance Windows File Compression can free up a lot of space - but
frequently it's not as much as you might expect, and there is cost.

Regarding the remark about built-in encryption, how does it differ from TrueCrypt in the scenario of forgetting the password/pass phrase?

If we lose the key the data remains encrypted unless someone can crack it. So apparently, the risk is pretty much the same. Or is it?

Forgetting your password is one thing. And yes, if you forget your password in TrueCrypt you're just as screwed there too.

I guess I've seen just enough instances of people creating new user accounts and deleting the old, or just somehow messing up their Windows user accounts and accidentally losing access to their encrypted data that it seems an unnecessary additional risk.

On top of that TrueCrypt containers are portable, platform independent and can be transferred in encrypted form. Not always true for Windows file system encryption - if you copy a file it travels unencrypted.

Windows filesystem compression has a role, I'm just saying you should understand the ramifications when choosing whether or not to use it.

-Leo

Nord Carls
August 5, 2008 10:52 PM

Thx but how do I uncompress them?

Just do what's displayed above, but make sure that the "Compress" checkbox is unchecked.

-Leo

William
January 9, 2009 8:14 AM

I am actually interested in doing teh reverse, uncompress. Is there a way to uncompress the files that were compressed as old compressed files. I activated clean disk and realized it was going to delete all my old compressed files, I then cancelled the action and later found a lot of my files to be blue in script. Does this mean those are all compressed files and if so, how do I uncompredd them?

-William.

Just uncheck the "Compress file" option in the file properties.

- Leo10-Jan-2009

David Downer
January 20, 2009 4:07 PM

Leo, thanks for some very useful information. I have just been battling with updating my McAfee protection and was disturbed to see all the file names in blue. Your webpage (which I found on Google) gave me the answer quickly and helpfully.

Juan
May 23, 2009 7:13 PM

Thanks, Leo! I was searching all day for an answer online, and all these "major websites" had zero idea, or rather their sites were difficult to navigate through if they did have an answer. I appreciate the help!

Michael B
February 8, 2010 12:25 PM

Some of the blue files are audio files I've compressed into mP3s. But others are audio files I have not compressed. Some are Cakewalk (the audio recording software I use) project files which I have not compressed. Often when I try to open these I get a message saying that audio has been replaced with silence and that the file cannot be found. When I open it, there is silence, and a straight line where there should be audio waves.
Considering the comment above about clean disk, if I have run disk defragmentation or disk check would those eliminate audio? I looked at the "compress files" command on some files as you indicated and found that "compress files" was checked, though I do not recall doing that since I didn't know about it! I unchecked them, the files now show in black but there is still no audio.

Vijay
March 29, 2010 10:19 PM

Thanks Leo, I was confused why my files were looking in Blue. I had windows XP SP2 and recently upgraded to SP3. After the upgrade some files were in blue. I assumed blue files were of little use and deleted several of them. But anyways, this is some useful info.

Vijay

perfb
February 22, 2011 12:02 PM

re compression adding extra work to read/write files - I have read that modern CPU's execute the compression algorithms much faster than the disk i/o (for non SSD disks), so that file compression may actually speed up file i/o from disk.

Missy
April 20, 2011 6:42 AM

THANK YOU SO MUCH! IT WAS VERY HELPFUL. I WAS SURPRISED WHEN I SEE MY FILES IN BLUE AND I ALMOST PANICKED. GOOD THING, I GOOGLED IT AND FOUND THIS ARTICLE! :)

Thanks for filling me in. It's appreciated, and you will be hearing from me again.

Lise
July 27, 2011 8:44 AM

Thank you....was starting to go wt??? when after IT worked on my computer all of a sudden I had blue all over the place...as stated earlier this was the answer and I was able to understand it! Thanks

Dawn Thorpe
January 12, 2012 1:12 PM

Why are some of my emails typed in blue while other parts of this email are in black?

Connie
January 12, 2012 6:43 PM

@Dawn
That is a feature of your email program. It is trying to help you distinguish between the part of the email you are typing, and the part that came from somewhere else. The colors being used can be changed in settings.

Jana Sheeder
May 10, 2012 12:11 PM

Phenomenal information! Thank you so much for clarifying this for me. I ran multiple programs overnight, and when I checked my computer this morning, many of the files were named in blue. WHEW! Thanks again.

Lori
May 13, 2012 4:50 AM

Not sure my question went in. So here it is again,plus a bit more. What happens if I delete the blue files? Because since they are there they are there all the sudden my computere is running majorly slow although I have lotsa space.

I would never EVER delete a file just because it's colored blue. It may still be an important file.

13-May-2012

Mark J
May 13, 2012 5:23 AM

@Lori
Some blue files may be critical to your computer's operation, so I wouldn't delete any of them unless I was sure I didn't need that file. Blue only means that they are compressed. It says nothing of their usefulness or importance.

Vedana Freitas
July 19, 2012 10:39 AM

Is this true of Word documents too? Some of my word docs are listed in blue - i have not compressed them that I know of. How do they get compressed without me compressing them?

As long as you're looking in Windows Explorer it doesn't matter what type of file they are - if they're blue the files are compressed when Windows places them on disk. The most common culprit is running Window's Disk Cleanup utility.

20-Jul-2012

Howard
January 3, 2013 2:07 PM

How do your decompress the files. I compressed some by accident and they were system files with passwords and other encrypted items. Now they will not function as they should.

Mark J
January 4, 2013 1:24 AM

@Howard
Select those files or folders you want to decompress, right click on one of those selected items, click the Advanced button and make sure the "Compress contents to save disk space" and the "Encrypt contents to secure data" boxes are unchecked. Finally click OK.

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